code: def __call__(cls):
      if cls.__instance is None:
          cls.__instance = super(_TzSingleton, cls).__call__()
      return cls.__instance
  
file_path: catboost/contrib/python/python-dateutil/py3/dateutil/tz/_factories.py
imports: from datetime import timedelta
  import weakref
  from collections import OrderedDict
  from six.moves import _thread
label_desc: Use image node_id 2 for calling the _TzSingleton obj's underlying member method code with example usage: obj.__call__(cls) and returns: cls